This invention relates to a well fluid sampling tool and to a well fluid sampling method.
The invention particularly, though not exclusively, relates to a so-called single phase or monophasic sampling tool, and related method.
There are many circumstances where it is desirable to sample a fluid material, whether as a gas, a liquid, or a mixture of the two, and determine its nature, for example, its physical and chemical composition, to determine information about the body of fluid from which the sample was taken. On some such occasions the sample may be obtained under one set of ambient conditionsxe2x80x94of pressure and temperature, sayxe2x80x94and thereafter removed to a quite different set for analysis such that, if unprotected, the sample""s statexe2x80x94e.g. its physical and chemical formxe2x80x94may change during this removal until it is no longer sufficiently representative of the original fluid. One typical example of this situation occurs when sampling fluids issuing from geological formations into which a well, such as an oil/gas well, has been drilled. At the bottom of the well, which may be several miles deep, pressure and temperature are highxe2x80x94possibly several hundred atmospheres, and in the low hundreds of degrees Celsius. Whilst the formation fluid may under these ambient conditions be a single phase fluid, nevertheless a sample of this fluid transported to quite different ambient conditions of the surface (specifically of pressure and temperaturexe2x80x94often referred to as NAP, Normal Atmospheric Pressure, or as NTP, Normal Temperature and Pressure), where it is to be analysed to reveal useful information about the well, may easily separate into two or more distinct phasesxe2x80x94for example, a liquid phase, a gas phase (originally dissolved in the liquid), and a solid phase (originally suspended or in solution in the liquid).
As such, the separated sample is no longer truly representative of the original fluidxe2x80x94or, at least, not in an easily-understood wayxe2x80x94and so has lost much of its value. Indeed in some circumstances it may be impractical to reconstitute the original fluid sampled.
Single phase sampling tools are known. For example, WO 91/12411 (OILPHASE SAMPLING SERVICES) discloses a well is fluid sampling tool and method for retrieving single-phase hydrocarbon samples from deep wells. In that document the sampling tool is lowered to the required depth, an internal sample chamber is opened to admit well fluid at a controlled rate, and the sample chamber is then automatically sealed. The well fluid sample is subjected to a high pressure to keep the sample in its original single-phase form until it can be analysed. The sample is pressurised by a hydraulically-driven floating piston powered by high-pressure gas acting on another floating piston. Once sampling is initiated e.g. by an internal clock, the entire sequence is automatic.
GB 2 252 296A (EXAL SAMPLING SERVICES) discloses an arrangement which is pressure compensated, so that as the container is lifted to the surface, and the ambient pressure and temperature drop, firstly the sample itself is sealed off to prevent it expanding (and separating) under the reduced pressure, and secondly the original ambient pressure is positively maintained despite any temperature change seeking to cause a corresponding pressure change (so that temperature-induced pressure drop and phase separation is avoided). This end is attained by a sampler wherein the sample chamber, in which the sample itself is received and stored, is sealingly closed at one end by a moveable partition to the other side of which is applied either directly or indirectly (via a buffer fluid) a source of suitably pressured gas.
The aforementioned sampling tools essentially use compensation techniques, i.e. the pressurised gases act on the sample to compensate for pressure drop in the sample due to temperature drop. These sampling tools, therefore, require the provision of a gas reservoir and complicated mechanisms to apply pressure to the sample to compensate for temperature reduction induced pressure changes.
SU 368 390 (MAMUNA et al) discloses a device for withdrawing samples of formation oil, including a body, a receiving chamber with a piston, and an inlet valve, wherein the receiving chamber is fitted with an electric heater connected to a thermometer mounted in the piston, with the aim of preserving the properties of the formation oil in the sample withdrawn.
WO96/12088 (OILPHASE SAMPLING SERVICES) discloses a well fluid sampling tool and method for retrieving reservoir fluid samples from deep wells. In this document the sampling tool is lowered to the required depth, an internal sample chamber is opened to admit well fluid at a controlled rate, and the sample chamber is then automatically sealed. The temperature of the sampled well fluid is maintained at or near initial as sampled temperature to avoid the volumetric shrinkage otherwise induced by temperature reduction, mitigate precipitation of compounds from the sample, and/or maintain the initial single phase condition of the sample. The sample chamber is thermally insulated, provided with a storage heater, electrically heated, given a high heat capacity, and/or pre-heated to sample temperature.
A problem with prior art single phase sampling tools is that the tool must be lowered, in use, down within a is drillstring. The tool must, therefore, be of less than a predetermined outer diameter. However, the tool should also be as short as possible, for example, to seek to avoid the tool becoming stuck or xe2x80x9changing-upxe2x80x9d within the drillstring.
It is an object of at least one aspect of the present invention to obviate or mitigate one or more of the aforementioned problems in the prior art.
It is a further object of at least one aspect of the present invention to seek to provide an optimum sized sample chamber within a tool of particular outer dimensions (outer diameter and length).
These objects are addressed by the general solution of providing a well fluid sampling tool with an evacuated chamber surrounding at least part of a sample chamber, an outer wall of the evacuated chamber being adjacent to or preferably forming an outer wall of the tool.
According to a first aspect of the present invention there is provided a well fluid sampling tool having, at least in use, a sample chamber at least partly contained within an at least partially evacuated jacket, an outermost wall of the jacket being adjacent to or forming an outermost wall of the tool.
In such a tool the evacuated jacket acts to maintain the sample as originally retrieved, e.g. in single phase form (at original temperature).
Advantageously the sample chamber is substantially contained within the evacuated jacket.
Preferably, the evacuated jacket comprises first and second tubular bodies, the first tubular body comprising the outermost wall of the jacket and the second tubular body being provided within the first tubular body, an evacuated chamber being provided between the two bodies.
Advantageously, the evacuated chamber is formed by a longitudinal annular space between the bodies.
The pressure in the annular space may be approximately between 10xe2x88x927 PSI and 10xe2x88x9211 PSI and typically around 10xe2x88x928 PSI.
Preferably, the first and second bodies are formed in one piece, being joined at least one end.
Preferably also, the sample chamber is provided with a third tubular body which is at least partly provided within the second tubular body.
Advantageously, sample temperature maintenance means are provided, preferably between the second and third tubular bodies.
Preferably, the temperature maintenance means include a plurality of heaters spaced longitudinally between the second and third tubular bodies.
Advantageously the heaters are sized to seek to compensate for heat loss at their respective locations.
Advantageously first and second heaters provided at first and second ends of the third tubular body are more powerful than heaters provided distal from the first and second ends. This arrangement is particularly advantageous so as to seek to compensate for heat loss from the ends of the sample chamber. Preferably the second heater is more powerful than the first heater.
Preferably the temperature maintenance means further comprises at least one temperature sensor for detecting the temperature of the fluid sample.
Preferably the at least one temperature sensor measures the temperature of an outer wall of the third tubular body.
Preferably the tool further comprises means for controlling admission of a sample into the sample chamber.
The admission control means may comprise a floating piston controllably moveable longitudinally within the sample chamber.
The admission control means may further comprise means for controllably moving the floating piston.
The controllable movement means may comprise a further fluid and means for controllably reducing pressure of the further fluid.
Preferably the piston is mounted on and moveable along a piston rod.
The piston rod may have a piston stop at one end adapted to limit travel of the piston at that one end of the piston rod.
The piston rod may further carry a plug at another end. Advantageously ends of the sample chamber are defined by he piston stop and the plug.
The tool may be provided with one or more sample inlet ports.
The tool may also be provided with one or more sample utlet ports, which outlet ports may be distinct from the inlet ports.
The tool may also provide means for removing a sample from the sample chamber.
The sample removal means may include first and second ports which communicate with first and second outer ends of the sample chamber. Thus, in use, a pump may be connected across the first and second ports so as to apply a differential pressure across the first and second ends of the sample chamber, thereby effecting movement of the sample chamber within the tool towards one or more sample outlet ports.
In use, a sample transfer vessel may be connected to the one or more sample outlet ports via one or more valves so as to allow controllable transfer of the sample from the sample chamber to the transfer vessel.
Advantageously the transfer vessel may include a further floating piston provided within a transfer chamber.
Preferably the transfer chamber is of substantially the same volume as the sample chamber.
According to a second aspect of the present invention there is provided a well fluid sampling method comprising the steps of:
providing a well fluid sampling tool having a sample chamber at least partly contained within an evacuated jacket, an outermost wall of the jacket being adjacent to or forming an outermost wall of the tool;
lowering the tool down a wellbore to a location where well fluid is to be sampled;
admitting a sample into the sample chamber by means of controllable admission means;
sealing the sample chamber;
retrieving the sample to surface while substantially maintaining the temperature of the sample;
removing the sample from the sample chamber into a chamber of a sample transfer vessel.
By such a method it is sought to maintain the sample as originally sampled, e.g. in single phase form (and at substantially original temperature).
This may be achieved as the sample chamber has a predetermined volume; thus by seeking to maintain the temperature of the sample the pressure of the sample is also maintained.
Advantageously on admitting the sample into the sample chamber temperature and pressure outside the tool are measured and stored by suitable measurement means and storage means.
According to a third aspect of the present invention there is provided a well fluid sampling tool including a sample chamber and an at least partially evacuated jacket surrounding at least part of the sample chamber, the evacuated jacket comprising first and second tubular bodies having an at least partially evacuated annular space therebetween, the first and second bodies being integrally formed with one another.
Preferably the first and second bodies are integrally connected to one another at least at or near first adjacent ends of each body.
Preferably such integral connection may be formed by welding, and advantageously e-beam welding.
Preferably also, the first and second bodies are connected to one another at or near second adjacent ends of each body.
Advantageously a centraliser may be provided between the first and second bodies, which centraliser may preferably be made at least partly from titanium.
According to a fourth aspect of the present invention there is provided a method of operating a well fluid sampling tool, the tool comprising a sample chamber, heater means in thermal communication with the sample chamber and means for controlling the heater means including means for measuring temperature external of the tool, the method comprising:
storing a preset temperature on the control means;
lowering the tool down a borehole;
continually monitoring the temperature external the tool at predetermined intervals;
comparing the measured external temperature to the preset temperature and if the measured external temperature is greater than the preset temperature then causing the heater means to heat at least part of the sample chamber to the measured external temperature.
Advantageously, as the tool is lowered if the external temperature is greater than the preset temperature then the external temperature is stored as the preset temperature.
Advantageously as the tool is lowered the pressure external the tool is also continually monitored, and preferably the highest external pressure monitored is stored on the control means.
In a preferred embodiment the tool includes an electronic clock circuit and a memory logger circuit.
According to a fifth aspect of the present invention there is provided a well fluid sampling tool including a sample chamber and pressure relief means communicating between the sample chamber and external the tool such that, in use, if pressure in the chamber exceeds a predetermined level the pressure is relieved via the pressure relieve means.
The pressure relieve means may comprise a pressure relief valve or a breakable disc. The tool may include sample temperature maintenance means.
Provision of the pressure relief means seeks to avoid excessive pressure build-up within the sample chamber, e.g. due to thermal runaway of the temperature maintenance means.
A tool according to any of the first, third or fifth aspects hereinbefore mentioned may be inserted into a borehole by wireline and may be coupled together with similar tools or with other tools, for example, memory pressure gauges, togging tools, spinners or the like, by threaded cross-overs.